The present invention relates to a soap bar plodder which produces marbleized soap bars made of a plurality of different colored soap materials including soap, synthetic detergent or mixtures thereof. For the sake of brevity the terms "soap", "soap bar" or "soap material" will be used to indicate the products of any of the above materials.
The inventor of the present invention previously disclosed a similar marbleized soap bar plodder in the published specification 47-3619 (3619/1972) in Japan. Said known plodder comprises: a horizontal cylinder which has a pressing chamber and a nozzle formed in front of said pressing chamber; two hoppers mounted on said cylinder, one being remote from said pressing chamber while the other is nearer, and; an extruding screw installed in said cylinder. Said extruding screw is formed as a single-thread screw under and adjacent to said remote hopper, and a second thread forming a double-thread screw is added from the part facing said nearer hopper to the front end of this extruding screw. The first thread groove is covered at the portion beneath the nearer hopper by a sealing wall which is formed integrally with the screw along the helical thread thereof and has the same outer diameter as the screw. Accordingly, the first soap material from the remote hopper passes through the space between said sealing wall and the first thread groove, whereby the second soap material from the nearer hopper can avoid being mixed with the first.
However, such a plodder has the following drawbacks. As the first soap material passes through the sealing wall along the helical thread, a large degree of frictional resistance is generated with the result that the required driving force increases and a large amount of frictional heat is produced.
Secondly, a large amount of back pressure is applied to the first soap material than to the second because of the frictional resistance generated inside the sealing wall. Accordingly, a larger amount of mechanical energy is applied to the first soap material than to the second, with the result that the viscosity, plasticity and hardness of the first soap material are different from those of the second. Consequently, the homogeneity and the desired degree of bonding to prevent cracking can not be attained with regard to a plodded soap bar consisting of two different soap materials.